1. Field of the Invention
The present invention relates to a probe and a method for attaching a particle to the apex of a probe tip, and relates more particularly to a probe and a method for attaching a conductive particle to the apex of a probe tip with the application of a bias voltage.
2. Description of the Related Art
Scanning probe microscopy (SPM) is applied for depiction or measurement of the details of fine-scale surface features and material characteristics, and such depiction or measurement is usually performed using a sharp probe tip to scan a target surface.
The probe tip is fixed to one end of a cantilever beam such that the probe tip can move following the profile of a target surface by means of the cantilever beam while scanning. During scanning, the probe tip moves up and down due to the weak interaction forces between atoms on the apex of the probe tip and on the target surface. By measuring the distances of the up-and-down movement, the profile of the target surface can be depicted or the surface characteristics of the target surface can be measured.
The resolution of an SPM tool is determined by the size of the apex of a probe tip. When the radius of curvature of the apex of a probe tip is smaller, the resolution of measurement is higher. If a probe tip with an apex having radius of curvature larger than the particle diameter of a molecule is utilized to perform measurement, the probe tip can only measure the average of the interaction expression of several molecules. Therefore, in order to measure the characteristics of a molecule, the size of the apex of a probe tip should be matched to the size of the target molecule. To achieve this, techniques for the attachment of a micro-particle or a nanoparticle have recently been the focus of much development.
Using a self assembly monolayer (SAM) as an adhesion means to attach a nanoparticle to the apex of a probe tip is one of several traditional techniques. For example, a paper by Vakarelski, I. U. et al., titled “Single-Nanoparticle-Terminated Tips for Scanning Probe Microscopy,” Langmuir (Letter), 2006, 22(7), pp 2931-2934, teaches a method that a colloidal gold nanoparticle of several dozen nanometers is attached to the top of an SPM probe tip using a wet chemistry procedure. However, the method requires several chemical processes to form an attach layer on the surface of the probe tip, and these chemical processes may increase the cross sectional area and the surface roughness of the probe tip. Furthermore, to attach nanoparticles of different materials or to use a probe tip of different material, different SAMs are required so that the application of the method is inconvenient. In addition, to attach a single nanoparticle to the top of a probe tip by the method requires careful control of parameters such as the concentration of nanoparticle suspension, the probe tip immersion time, and the method of immersing the probe tip, and such parameters are difficult to control during mass production.
A paper by Okamoto, T. et al., titled “Photocatalytic deposition of a gold nanoparticle onto the top of a SiN cantilever tip,” Journal of Microscopy 2002, (2001): 101-103, discloses a method that initially coats a titanium dioxide layer on the surface of a probe tip, and then exposes the titanium dioxide layer immersed in a solution including gold ions to light. When the titanium dioxide layer immersed in a solution including gold ions is subject to optical exposure, the excited electrons in the conduction band reduce gold ions into gold metal. Illumination by an evanescent wave generated with a total reflection configuration limits the deposition region to the very tip. Because the method requires an illumination system that can generate the evanescent wave and equipment for depositing titanium oxide, the manufacturing cost of the probe tip fabricated by the method is high. In addition, the method cannot precisely control the size of the deposited gold particle, and therefore, it is difficult to maintain good quality control.
In summary, there is no method that can be applied to attach a particle to the top of a probe tip that has no unwanted effects and that is cost effective for utilization by the industry.